Another Montreal must! Schwartz's is the Katz's deli (in NYC) of Montreal. It's a simple deli that's been around for ages and still only makes the classics. They also sell a variety of seasonings so you can make their classics too. Also important to note, it's a Jewish deli but not a kosher deli.
There are two sides - sit down and takeaway. If you're in a rush or it's a nice day, definitely jump on the takeaway line and grab the smoked meat (brisket) sandwich to go. It's a few blocks from Mont Royal Park so you can bring your food there, or find a seat at ledges across the street. I haven't dined in the real restaurant since I have a strong aversion to waiting on lines, but it's the same classics so I'd recommend the take away.
The sandwich is simple with just the warm smoked brisket, spiced to perfect, and a touch of mustard. I'm not a huge mustard fan and thought the touch of it was perfect. Enjoy!!